Displaying image part over navbar

Site URL: https://www.beverenbuiten.be/

Hi everyone, 

I have the Website www.beverenbuiten.be and I want to display the dates part over the navigation bar. I moved the image already up so it is in the right place but I can't seem to put it on top of the navbar. 

I tried already working around with z-index and I can put the whole section in fron of the navbar but when trying to put only the image I can't seem to figure it out.

( I tried putting the z-index higher as the navbar z-index). 

Can somebody tell me how I can do this ? 

In attatchement the design on how it should look.

Thanks in advance